Forensic Biology
The Forensic Biology section examines evidence for biological material from a variety of case types, including, but not limited to, homicides, sexual assaults, assaults, burglaries, hit‑and‑run incidents, and criminal weapon possession. Biological material may be present on items such as clothing, weapons, bedding, cigarettes, condoms, bottles, or any object handled or left behind at a scene. These materials may have blood, semen, saliva, skin cells, or hair, which are sources to recover DNA.
The laboratory analyzes samples from over 50 different law enforcement agencies throughout Westchester County. The Forensic Biology section accepts evidence submitted by police agencies and the Westchester County District Attorney’s Office.
Biological Evidence
When submitted to the laboratory, biological evidence is secured in a walk‑in cold room before being assigned to an analyst. The laboratory has multiple examination rooms for documenting, testing, and sampling evidence. An alternate light source (ALS) may be used to locate potential stains, which can then be screened with presumptive tests for blood, semen, or saliva. Stains that test positive may undergo additional testing, including DNA analysis. Some DNA‑containing materials, such as skin cells or hair, are not suitable for presumptive screening and can proceed directly to DNA testing.
To compare evidence DNA profiles, reference samples are required from victims, suspects, or others who may have deposited DNA at the scene. These references are typically collected as buccal swabs from the inside of the cheek.
DNA Analysis
The Forensic Biology section conducts DNA STR (Short Tandem Repeat) analysis, a method that provides rapid results, strong distinguishing power, and the ability to examine small or degraded DNA samples. Examples include tissue on a pulled hair or skin cells collected from beneath a victim’s fingernails.
DNA analysis involves four main steps: DNA is first extracted from cells, and the total amount recovered, including any male‑specific DNA, is measured. The DNA is then amplified through Polymerase Chain Reaction (PCR) to produce millions of copies. These amplified fragments are separated and detected by capillary electrophoresis, and the resulting profiles are assessed for suitability for comparison. When a profile is suitable, a statistical calculation is performed to evaluate the strength of the association between the evidence and an individual reference sample.
The laboratory performs both autosomal and Y‑chromosome STR testing, which is particularly useful in sexual assault cases involving multiple male contributors or lower amounts of male DNA relative to female DNA.
CODIS
The Forensic Biology section participates in the FBI’s CODIS (Combined DNA Index System), a network of local, state, and national DNA databases. The section maintains the local crime scene DNA database for Westchester County and can compare unknown crime scene profiles to other unsolved cases across the county, state, and country, as well as to convicted offender databases. CODIS associations aid investigators in different jurisdictions by identifying potential links between cases early in an investigation. The system also includes dedicated indexes for unidentified human remains and missing persons.
Additional Services
Vehicle Processing
To facilitate the examination of cars and other vehicles, the laboratory is equipped with a secure forensic garage.
NAMUS-National Missing & Unidentified Persons System
The Forensic Biology section participates in NAMUS, which is utilized as a national repository for missing, unidentified, and unclaimed persons cases.
IGG-Investigative Genetic Genealogy
The Forensic Biology section assists in IGG investigations to aid in solving cold cases by identifying distant DNA matches or unidentified human remains.